The invention relates to power-driven conveyors generally and, more particularly, to spiral belt conveyors and methods for transporting articles up and down helical paths.
Conveyor belts are often used to convey articles, such as foodstuffs and other materials, through cooled or heated environments. Spiral conveyors, in which a conveyor belt follows a helical path winding around a central tower, are used in freezers and ovens to provide a long conveying path with a small footprint. Low-tension spiral conveyors, in which the conveyor belt is driven by frictional contact between the outside of a rotating tower, or drum, and the inside edge of the belt, are conventionally used in these applications. Increasing the dwell time of articles in a freezer or oven or feeding and discharging articles at the same level may be achieved by advancing the conveyor belt along two helical paths—one going up and the other going down. But two separate spiral conveyors take up more than twice as much floor space as a single spiral conveyor. If limiting floor space is important, a double-helix spiral conveyor may be used. Some double-helix spiral conveyors use two concentric drive drums having different radii to frictionally drive the conveyor belt helically up the outside periphery of one of the drums and down the other. But these double-helix spirals have a complex cage structure to connect the inside of the drum to the central drive column and provide the structural rigidity needed to maintain the shape of the drum. Furthermore, the two drums and the extensive support structure interfere with airflow through the conveyor and affect the efficiency of the freezer or oven.